I know that the universe is 13 billion years old and the fastest anything could be is the speed of light so if the universe is expanding as fast as it could be wouldn’t the universe be 13 billion light years big? But I’ve searched and it’s 93 billion light years big, so is the universe expanding faster than the speed of light?
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The expansion of the universe doesn’t have a *speed*–speed depends on space (length) and it’s space that’s changing, so speed doesn’t make sense.
Expansion does have a *rate*, but it’s not measured in distance-per-time, it’s speed-per-distance. Specifically, 73.24 (km/s)/Mpc.
What that means is that *expansion* isn’t “moving” faster than light (that’s apples and snorkels), but **the distance between** two objects may be ~~moving *away from each other*~~ **increasing** faster than light.
Tl;dr: The “speed” of anything doesn’t make sense from the position of expansion because it’s space that is changing.
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